MOSCOW -- A Moscow court has extended the pretrial detainment period for several of the 24 Ukrainian seamen who were jailed after the Russian Coast Guard seized their vessels near the Kerch Strait in a flare-up of tensions in November.

On April 17, the Lefortovo district court was hearing requests by prosecutors to keep the seamen in jail pending further investigation and trial.

With relatives of the seamen attending hearings conducted in three separate courtrooms, judges had prolonged pretrial detention until July 24 for 12 of the sailors by midafternoon.

Outside the courthouse -- which bears the same name as the jail where the Ukrainians are being held, Lefortovo -- a lone protester held a sign that read, 'Free the Ukrainian sailors.'

On November 25, Russian Coast Guard vessels fired on and seized three Ukrainian Navy vessels and their crews while they were on their way from the Black Sea to the Ukrainian port of Mariupol, on the Sea of Azov.

Moscow accuses them of illegal entry into Russian territorial waters, which they deny, and they are formally charged with illegal border crossing.

The incident increased tension over the Kerch Strait, which is the sole passage from the Black Sea to the Sea of Azov.

The strait runs between Russia and Crimea, the Ukrainian peninsula that Russia seized in March 2014 after sending in troops and staging a referendum deemed illegitimate by Kyiv, the United States, and a total of at least 100 countries.

The takeover of the peninsula, and Russian support for separatist militants who seized parts of eastern Ukraine at the start of a conflict that has now killed some 13,000 people, came after pro-European protests pushed Moscow-friendly Ukrainian President Viktor Yanukovych from power in Kyiv.

Western leaders have demanded that Russia release the seamen and the incident has led to the imposition of additional sanctions on Russia.